A metal-oxide-semiconductor (MOS) transistor is one of the most important devices in modern integrated circuits. A MOS transistor usually includes a semiconductor substrate, gate structures on a surface of the semiconductor substrate, and source/drain regions in the semiconductor substrate on sides of each gate structure. Each gate structure includes a gate dielectric layer on the surface of the semiconductor substrate and a gate electrode layer on a surface of the gate dielectric layer.
In a MOS transistor, a voltage is applied to a gate structure, to regulate channel currents under the gate structure and generate on/off signals.
However, performance of conventional semiconductor devices formed by the MOS transistors still needs improved.